Method for mineral separation



Oct. 2, 1956 N. GOODWIN 2,765,075

METHOD FOR MINERAL. SEPARATION Filed March 16, 1955 zap We 33 32 W),- [25 o n n n (1 J U A? l INVENTOR. NOR/PIS aooom/v BY M i wm A T TORNEV United States Patent lVlETI-IOD FOR NIINERAL SEPARATION Norris Goodwin, San Francisco, Calif., assignor to Centrijig Corporation, San Francisco, Calif., a corporation of California This invention relates to primary separation, and, particularly, to rough or preliminary mineral concentrations for continuously separating the heavy mineral content of a large volume slurry.

The recovery of valuable minerals from sands of various types has become a major industry. Among the many instances may be mentioned the recovery of ilmenite, zircon, rutile, and monazite from Florida beach sands and similar sands in Australia and India. Also, the recovery of monazite, ilmenite and zircon from lake bed sands of Idaho and the recovery of phosphate from the Florida beds. In some instances, such as that encountered in the Magdalena area of Baja California, both phosphate and valuable heavy minerals are found together. Under these conditions it is highly desirable to remove the heavy mineral fraction before the balance of the sands are treated for the recovery of the phosphate minerals (cellophane) by flotation.

In all instances very large volumes of sand must be treated since the heavy mineral content of value may represent only a few pounds per ton, as little as one to three pounds in the case of monazite. Economic separation on large scale operations such as these entail, is

greatly benefited by a simple, cheap means of separation of the heavy minerals which are all concentrated in a small fraction of from one to ten percent depending on the sand.

Of all of the heavy minerals present in sands, magnetite is the only one that has been successfully removed by magnetic means from wet slurries. Unfortunately, in most of the instances cited, magnetite represents only a minor fraction of the heavy minerals present and its separate and individual removal from the total flow is an unwarranted expense. Furthermore, the conventional methods of magnetic separation lift or pull the magnetite particles away from the attendant sands, leaving most of the heavy mineral content. heavy minerals be completely removed before separating the main volume of valuable components, such as phosphates.

It is an object of the present invention to provide a preliminary or preparatory concentration and separation by removing all of the heavy mineral content of such beach sands and the like, whether magnetic or nonmagnetic.

It is an object of the present invention to remove not onlythe magnetite but the other heavy mineral constituents by causing the magnetite to coalesce into a coherent mass induced by lines of magnetic force, thereby entraining or binding nonmagnetic particles with the magnetic, andseparating such coherent mass from the balance of the unwanted sands, provision being made for increasing the proportion of magnetite in the sands in such cases as there is a natural deficiency.

It is also an object of the present invention to provide a method and process for separating substantially all of the heavy mineral content of a slurry of sands containing It is most desirable that the 2,765,075 Patented Oct. 2, 1956 ice heavy minerals, whether magnetic or nonmagnetic, by a magnetic classification.

It is also an object of the present invention to provide a method and apparatus for magnetic separation of the heavy mineral content, including both magnetic and nonmagnetic heavy minerals, recovering the magnetic mineral which is most active and returning the same to the feed in a closed circuit.

Another object of the invention is the provision of a method and apparatus for the separation of the heavy mineral content, both magnetic and nonmagnetic, continuously from feeds and slurries involving large volume deliveries.

A further object of the invention is to provide a meth 0d and apparatus for the recovery of substantially all of the heavy mineral content from sand slurries and the like, and to do so continuously.

It is another object of the invention to continuously remove the heavy mineral content of a slurry of sand and the like, without subjecting the separated material to any washing action at the time of separation.

Further objects are to provide a method and apparatus for carrying out the same of maximum simplicity, economy of operation, and which will require minimum supervision and maintenance, also such further objects, advantages and capabilities as will more fully appear herein and as are inherently possessed by the invention described herein.

The invention is illustrated diagrammatically in the accompanying drawings, and while there is shown therein a preferred embodiment thereof, it is to be understood that the same is merely illustrative of the invention and that the invention is capable of modification and change and comprehends other details, without departing from the spirit thereof or the scope of the appended claims.

Referring to the drawings:

Figure l is a schematic flow diagram of the method and apparatus of the present invention; and

Figure 2 is a schematic drawing of the magnetic drum and its location with respect to the sluice outlet and tailings delivery.

Referring now more particularly to the drawing, in which like reference numerals indicate like parts in the several views, and with particular reference to Figure 1, there is shown a complete closed circuit system for operating the invention. The sluice box it) accepts the delivery of a suitable slurry of sand containing heavy minerals, such as ilmenite, rutile, zircon, monazite, and magnetite. The sluice box 10 is angled downwardly with the amount of the angularity being dependent upon the nature of the minerals involved, the particle sizes, and their proportionate content in the slurry. Obviously, the coarser the sand, the steeper the angularity of the box. It has been found that for most beach sand passing a 65 mesh screen and having a heavy mineral content of from 1% to 4%, the slope is from one-half inch to one inch per linear foot. The angularity should be adjusted to that where the heavy minerals will stratify and how but will not settle and pack in the bottom of the sluice box. The sluice box may be provided with rifiles if needed or any other means for securing stratification. Likewise, it should be understood that any means of stratifying classification may be substituted for the sluice box, such as jigs, shaking tables and the like. A continuous belt 11 passes over pulleys 12 and 14 with the upper travel of the belt 11 being just below the sluice box 10, parallel therewith and adjacent the delivery end 15. The pulley 14 may be slightly larger than the pulley 12 as this is what is known in the art as a magnetic pulley. The pulleys l2 and 14 and the belt 11 are substantially the same width as the sluice box 10.

Within the pulley 14 is a rotating magnet 16 disposed 3 radially and which is so positioned as to act over the entire width of the belt 11. The magnet 16 may be either a permanent magnet or an electric magnet as shown, dend ntl p n. v a i ity. Powe a the k h heavy minerals, both magnetic andn'onrnagnetic, are removed at this point, collected on the belt 11 and are delivered to the collector 17, from whence they go by line 18 to the submerged belt-type magnetic separator generally designated 20, which niay be a commercial standard typesuch as a Crockett or Jefiry separator. In the equipment 20 water is added by line 21 to the incoming feed of heavy minerals and from this slurry, which is substantially all of the heavy mineral content of the originalfeed in sluice box 10, the magnetic heavy minerals are lifted to the belt 22 and are carried thereby until released over the collecting hopper 23. Since the magnetite is by far the most sensitive to this selection, the portion carried by the belt 22 will be substantially only magnetite. It maybe noted that in this magnetite recovery separator 20, the magnetite is lifted from the stream and must pass upwardly against gravity, through relatively clear water, leaving the nonmagnetic particles behind. The magnetic trapping which is the subject of the separation disclosed. pulls the magnetized magnetite downward to form a mat or coherent mass in what is essentially the bottom of the sluice, .entangling and trap ping the other heavy minerals including the nonmagnetic particles, and permitting their removal as a substantially complete fraction, from the system. Pump 24 delivers the magnetite along line 25, where it is redelivered to the system in a closed circuit. The nonmagnetic or only weakly magnetic heavy minerals, not being affected by the belt 22, flow into collecting hopper 26 and are delivered by line 27 as concentrates.

With respect to Figure 2, the radial location of the magnet 16 is of importance. As will be observed, the delivery of a liquid, with or without entrained solids, will produce :1 characteristics arch. The delivery line of the liquid is indicated diagrammatically as line 28. The flow will continue in substantially the same plane until the force of gravity begins to operate to produce a downward curve. The length of the substantially straight portion at the delivery end will be longer or shorter, depending upon the speed of the flow. The volume of How does not change the characteristics to any great degree, this being largely determined by the slope of the box. The length of the straight portion of the delivery end of the flow 28 is estimated from the working conditions and the magnet 16 is placed substantially perpendicular thereto, which point is also the tangent of the circle defined by the pulley 14.

Operation The following are typical analyses of sands from different parts of North America which are of great interest at present:

Florida-Trail Ridge (average 365 samples):

Percent Clay, etc 5.77 Sand (quartz and feldspar) 90.80 Heavy mineral 3.35

Heavy mineral con-tent:

Ilmenite (leucoxene) 6.10% or 4 lbs. per ton. Ruti le 2.30% or 1.5 lbs. per ton.

Zircon 14.86% or l01bs. per ton.

4 Heavy mineral content:

Ilirienite 6.4% or 28 lbs.'pe'r ton. Rutile 0.18% or0.8 lb. per ton. Zircon 0.73% or 3.0 lbs. per ton. Sphene 1.5% or 6.8 lbs. per ton. Magnetite 6.6% or 30 lbs. per ton.

IdahoLong Valley:

Percent Clay, etc 5 Sand (mainly quartz) 93.5 Heavy minerals 1.5 Heavy m'iiieral content:

Ilmenite, garnet,

zircon, etc or 27 lbs. per ton. Monazite 10% or 3 lbs. per ton.

Magnetite Trace.

In describing the operation of the apparatus for carryi ng out the method for mineral separation, beach sands from Baja California, which are rich in heavy minerals, will be used. p

It will be observed that the beach sands show that about 75% of the products have a gravity less than 3.0 and include feldspar, silica and collophane (phosphate). About 10% are waste products having a gravity from 3.0 to 3.9 and include ferromagnesians, such as amphibole, pyro tene etc. They also comprise about 15% heavy minerals, including ilmenite, rutile, garnet, zircon, magnetite and others. The present method and apparatus is primarily concerned with the separation and removal of the 15% fraction of heavy minerals. Of the minerals eon-tainted in this analysis, magnetite is strongly magnetic, ilnienite has about half of the magnetic attractability as magnetite, and the remaining heavy minerals are weakly magnetic or nonmagnetic. It is to be noted that all of the heavy minerals generally encountered are variable in composition and hence variable in magnetic susceptibility. It will, therefore, beobserved that in accordance with the present engineering practice and tenaite's, only ia small portion of the heavy mineral content of such a slurry eould, ideally, be removed by magnetic separation, and, therefore, would not be a practical or eitective way to remove 211,6? substantially all of the 15% heavy mineral content.

The raw rnaterial 'of beach s an d, just as it comes from the dredgepump and at the full rate and volume of the delivery'of the pump, eriters as the feed 30 at the feed end of the sluice sex 10. When the operation is commenced, sufficie nt magnetite is added to the feed 30, so that the voliinieof magnetite is not less than equal to the entire nonmagnetic orweakly magnetic heavy mineral cefitii't'bf the new. Accordingly, if the heavy mineral content; bf the flow other than magnetite is 10%, then an equivalent volume of magnetite is added. It has been found desirable to add eitra fiiagne fite not to exceed 10% to riiake eefiaiii'iaere is always an excess voliime of magnetite. In the travel of the flow down the incline of the sluice 56x 10, the heavy minerals will form a layer dose to the bottom which is relatively free of gan'gue. This stratifiea'tion 'conti'riiies in the flow and is maintained at the discharge end 15. The now leaving the sluice box 10 passes just above the surface of the belt 11 on the 'rfiagnetiep ue' 14'. The belt 11 and the puney 14 are set f6 travel at a linear tind'pripheral speed which is appreiiuiatly efii lal to that of the peed of the of siisp'e'iided minerals 'at the point of discharge. This is important because, as will be readily understood, the y bf s d prevents iiy Washing action of the with r'as ea to the heavy minerals at the time of removal.

\ As the stratified flow comes under the influence of the magnet along'the line 28, substantially only the magnetite is arrested. Under such' influence the magnetit e par-titles forma n'etivorli bf dipole chains Whieh bind the nonmagnetic heavy minerals into a substantially solid mat, which literally pulls the entire heavy mineral content from the flow. The dendritic chains or trees formed by the magnetite under the influence of the magnet 16 entrap and physically bind substantially all of the heavy mineral content or layer, into a mat-like mass at the time of removal. It is also known that ilmenite particles, under circumstances such as are here present, will take positions in the chains of magnetite particles and so assist in the removal under magnetic conditions. The flow, with substantially all of its heavy mineral content removed in this manner, passes out of the system for further treatment, such as the removal of phosphate bearing minerals by flotation or other means.

As the pulley 14 rotates, the belt 11, with its mineral content burden, moves out and away from the influence of the magnet 16 and the heavy minerals are free to drop under the influence of gravity. The materials so released are collected in the hopper 17. Since magnetite or some other suitable magnetic mineral is required for the operation of the present method, its recovery and return to the system is of importance. Accordingly, the heavy mineral content which has been removed and collected in hopper 17 with its magnetite content passes by line 18 into any of the standard and commercial magnetic recovery separators, such as a Crockett submerged-belt separator or a Jeffry separator, which is designated 20. Before passing into this equipment, however, the heavy mineral content is formed into a slurry by adding water from line 21. It is this slurry which is delivered to the separator 20. In this type of equipment a continuous belt 31 passes over pulleys 32 and 33. On the under travel 34 the slurry is subjected to stationary magnets, which are designated diagrammatically as 35. The slurry of minerals from line 18 and added water from line 21 are fed into the equipment 20 so that immediately the flow comes under the influence of the magnet 35. That portion of the slurry which is strongly magnetic will be attracted to the under travel 34 of the belt 31 and will be carried thereby until the magnetic influence ceases, whereupon it will drop into the collecting hopper 23. Since magnetite is the only component of the heavy minerals which is strongly magnetic, substantially only magnetite is thus removed from the slurry. The remainder of the slurry is collected in hopper 16 and passes by line 27 as concentrates for other treatment and recovery.

The magnetite so removed is pumped by pump 24 along line 25 to make it available for return to the system in a closed circuit. As magnetite tends to retain its magnetism for a considerable period of time, a demagnetizing coil 29 is introduced in the return line 25. This is a simple solenoid energized with alternating current such as is common to the industry. Such demagnetization prevents flocculation of the magnetite particles and allows them to disperse in the sluice box. Inasmuch as the analysis shows some magnetite present in the original feed material, there is a slight gain in volume in the recovery just indicated, so that in the return of the recovered magnetite less added magnetite is required from the outside to make up the necessary volume. In a reasonably short period of operation, there is suflicient accumulation of this gain so that it is not necessary to add any magnetite from an outside source, making the entire circuit complete and closed. In fact, it is necessary as operation continues, to bleed off magnetite from each step in order not to unbalance the operation by the addition of too much magnetite to the system at the inlet. This factor, of course, depends entirely upon the magnetite content of the sand being treated.

It will be observed that a method of removing substantially all of the heavy minerals has been accomplished in a continuous manner and that the removal is not subject to the requirement of a limited flow, but is quite capable of handling large volumes continuously. Furthermore, especially where permanent magnets are used, the system requires very little power and only that for driving the pulleys for the two belts of the system, the pump and the demagnetism coil. The problem of pure water does not enter into the operation of this system because it will operate just as well on salt water as it will on fresh water. Tests indicate that substantially all of the heavy mineral content is removed, whereas by previous methods only about 70% could be removed by the known methods.

While the method has been described as using magnetite, it is to be understood that any other suitable material may be used such as ferrosilicon.

I claim:

1. The method of removing the heavy mineral content in large volume slurries of beach sands and the like, comprising adding to the slurry feed a volume of magnetic heavy mineral substantially equal to the volume of the nonmagnetic and weakly magnetic heavy minerals in said slurry, stratifying said heavy minerals into a bottom layer in said feed, subjecting said stratified feed to a magnetic field to remove substantially all of the heavy mineral content, forming a slurry of said separated heavy mineral content, recovering and removing the magnetic portion only of said heavy minerals from said last named slurry, demagnetizing said recovered magnetic mineral, and returning the proper amount of said magnetic heavy mineral to said feed slurry.

2. The method of continuously removing the heavy mineral content in large volume slurries of beach sands and the like, comprising continuously adding to the slurry feed a volume of magnetic heavy mineral substantially equal to the volume of the nonmagnetic and weakly magnetic heavy minerals in said slurry, stratifying said heavy minerals into a bottom layer in said feed, continuously subjecting the delivery of said stratified feed to a magnetic field to remove substantially all of the heavy mineral content, forming a slurry of said separated heavy mineral content, recovering and removing the magnetic portion only of said heavy minerals from said last named slurry, demagnetizing said recovered magnetic mineral, and contiuuously returning the proper amount of said magnetic heavy mineral to said feed slurry.

3. The method of continuously removing the heavy mineral content in large volume slurries of beach sands and the like, comprising continuously adding to the slurry feed a volume of magnetite substantially equal to the volume of the nonmagnetic and weakly magnetic heavy minerals in said slurry, stratifying said heavy minerals into a bottom layer in said feed, continuously subjecting the delivery of said stratified feed to a magnetic field to remove substantially all of the heavy mineral content, forming a slurry of said separated heavy mineral content, recovering and removing the magnetite only of said heavy minerals from said last named slurry, demagnetizing said recovered magnetite, and continuously returning the proper amount of said magnetite to said feed slurry.

4. The method of making the separation of the heavy mineral content from large volume slurries containing the same, comprising the steps of adding a magnetic heavy mineral to the feed slurry equal in volume to that of the nonmagnetic heavy mineral content, subjecting the feed slurry to initial stratification to form a layer of heavy minerals, passing the flow directly over a magnet to magnetically trap substantially all of the heavy minerals by means of the magnetic components of the heavy mineral content, subjecting the heavy minerals so trapped to a magnetic recovery separator in a slurry to remove the magnetic components of said heavy minerals, and demagnetizing said recovered magnetic heavy minerals.

5. The method of continuously making the separation of the heavy mineral content from large volume slurries containing the same, comprising the steps of continuously adding a magnetic heavy mineral to the feed slurry equal in volume to that of the nonmagnetic heavy iriineral content, subjecting the feed slurry to initial stratificatio'n to form a layer of heavy minerals,'passing the flow directly over a magnet to continuously magnetically trap substantially all of the heavy minerals by means of the magnetic components of the heavy mineral content, subjecting the heavy minerals so ti'apped to a magneticrecovery separator in a slurry to continuously remove the magnetic components of said heavy minerals, and continuously demagnetizing said recovered magnetic heavy minerals for return to said feed.

6. The method of continuously making the separation of the heavy mineral content from large volume slurries containing the same, comprising the steps of continuously adding magnetite to the feed slurry equal in volume to that of the nonmagnetic heavy mineral content, subjecting the feed slurry to initial Stratification to form a layer of heavy minerals, passing the flow directly over a magnet to continuously magnetically trap substantially all of the heavy minerals by means of the magnetite, subjecting the heavy minerals so trapped to a magnetic recovery separator in a slurry to continuously remove the magnetite, and continuously demagnetizing said magnetite for return to said feed.

7. In a moving stream containing heavy minerals of which a substantial portion is magnetic mineral, the method of removing the heavy mineral content comprising the steps of passing said stream directly over a moving belt on a magnetic pulley to form a mat of said heavy mineral content, pulling the said mat downwardly away from the main stream to the belt under magnetic force, said belt and said magnetic pulley being moved at the same linear speed as said stream, and separating the magnetic portion of the heavy mineral content from the nonmagnetic portion.

8. In a moving stream containing heavy minerals of which a substantial portion is magnetic mineral, the method of continuously removing the heavy mineral content comprising the steps of passing said stream directly over a moving belt on a magnetic pulley to form a mat of said heavy mineral content, continuously pulling the said mat downwardly away from the main stream to the belt under magnetic force, said belt and said magnetic pulley being moved at the same linear speed as said stream, continuously separating the magnetic portion of the heavy mineral content from the nonmagnetic portion and demagnetizing the same.

9. In a moving stream containing heavy minerals of which a substantial portion is magnetite, the method of continuously removing the heavy mineral content comprising the steps of passing said stream directly over a moving belt on a magnetic pulley to form a mat of said heavy mineral content, continuously pulling the said mat downwardly away from the main stream to the belt under magnetic force, said belt and said magnetic pulley being moved at the same linear speed as said stream, and continuously separating the magnetite from the nonmagnetic portion of the heavy mineral content.

No references cited. 

1. THE METHOD OF REMOVING THE HEAVY MINERAL CONTENT IN LARGE VOLUME SLURRIES OF BEACH SANDS AND THE LIKE, COMPRISING ADDING TO THE SLURRY FEED A VOLUME OF MAGNETIC HEAVY MINERAL SUBSTANTIALLY EQUAL TO THE VOLUME OF THE NONMAGNETIC AND WEAKLY MAGNETIC HEAVY MINERALS IN SAID SLURRY, STRATIFYING SAID HEAVY MINERALS INTO A BOTTOM LAYER IN SAID FEED, SUBJECTING SAID STRATIFIED FEED TO A MAGNETIC FIELD TO REMOVE SUBSTANTIALLY ALL OF THE HEAVY MINERAL CONTENT, FORMING A SLURRY OF SAID SEPARATED HEAVY MINERAL CONTENT, RECOVERING AND REMOVING THE MAGNETIC PORTION ONLY OF SAID HEAVY MINERALS FROM SAID LAST NAMED SLURRY, DEMAGNETIZING SAID RECOVERED MAGNETIC MINERAL, AND RETURNING THE PROPER AMOUNT OF SAID MAGNETIC HEAVY MINERAL TO SAID FEED SLURRY. 